Effect of nonsuperconducting secondary inclusions on the magnetization relaxation in melt-processed RBa2Cu3O7−δ (R=Nd and Yb) bulk superconductors at high temperatures

Abstract

We have studied the effect of nonsuperconducting inclusions on the magnetization relaxation in melt-processed $R{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ $(R=\mathrm{Nd}$ and Yb) bulk superconductor in a high-temperature region $(77\mathrm{}<~T<~90\hspace{0.5em}\mathrm{K}).\mathrm{}$ It is found that nonsuperconducting inclusions are mainly effective in reducing the normalized relaxation rate S $(\equiv -d\ln M/d\ln t)$ at low fields $\left[b_{\mathrm{irr}}\right(\equiv {\mu }_0{H}_a{/B}_{\mathrm{irr}})\lesssim 0.1]$ and at high fields ${(b}_{\mathrm{irr}}\gtrsim 0.4).$ A suppression in S is observed in an intermediate field region $(0.1\mathrm{}\lesssim b_{\mathrm{irr}}\lesssim 0.4)$ for the samples exhibiting secondary peak effect, suggesting a relation between the peak and the suppression.